1. Field of the Invention
The present invention relates to manufacturing of read-only memory media, and relates, in particular, to a holographic memory card that is portable and has a much higher memory capacity than magnetic cards or IC cards. Such a card would be useful in many applications including e-commerce transactions for identification purposes, because the card is difficult to copy or counterfeit, and in reproduction of music and video recordings and computer softwares, because of its high memory capacity and low cost in mass production.
2. Description of the Related Art
Pocket-sized information cards that can be carried with a person, such as bank cards based on magnetic strip recording of individualized data, have been in wide general use. Also, in recent years, integrated circuit (IC) cards have been considered for use in e-commerce for identification purposes.
Magnetic cards are low in cost but they can easily be counterfeited, and IC cards, though difficult to counterfeit, suffer from the disadvantage of high cost of bits.
In the meantime, information storage medium based holographic technology is being evaluated, because of its high memory capacity and difficulty of counterfeiting. Holography can be considered in terms of features that can be gained by using a planar hologram versus volume hologram. Volume hologram is superior in memory capacity but is lacking in proper technology for information transfer and is not suitable for mass production. Therefore, it is difficult to be applied to read-only memory media such as identification cards and softwares for distribution.
As for the planar hologram, mass production based on printing technology is possible but the memory density is restricted, and considering the problems posed by current apparatus for image reproduction, it is less attractive than IC cards. To counter the problem of memory density, laminated holograms may be considered for increasing the memory capacity, but the existing methods of data reproduction suffers from the problem of cross talk, which causes interference of a desired hologram image by the images from holograms stored in other recording layers.
It is an object of the present invention to provide a read-only recording medium that provides a high memory capacity and is capable of selective reading of a recorded layer and is amenable to mass-production at low cost.
The object has been achieved in a laminated optical medium for read-only information recording comprised by a plurality of information recording layers structured by planar waveguides having periodic light scattering factor formed so as to generate scattered light by injecting an input light into a waveguide, wherein the planar waveguides are made of polymeric materials.
The present read-only information recording medium of ultra-high memory capacity enables to provide a level of memory capacity that is equivalent to the capacity achievable by volume holography, using a low-cost planar holographic technique. The laminated medium is simple and energy conserving, because it does not require rotation mechanisms for reproduction of music and video holographic recordings. The medium is ideally suited as identification card, because the card is difficult to counterfeit and a high level of extra information can be stored conveniently for use in a wide range of potential applications.